Spondylolithesis is a type of spinal deformity where one vertebral body is displaced relative to another adjacent vertebral body. There are a number of treatment strategies for spondylolithesis including non-surgical treatment strategies and surgical treatment strategies. While non-surgical treatment strategies are typically implemented first, the condition can worsen and the non-surgical strategies may not prove to be successful in given cases. Also, the severity of the condition may be such that the non-surgical strategies are practically speaking not a viable option.
Surgical treatment strategies for these deformities typically incorporate the concept of reduction of the spondylolithesis and stabilization of the segment. In the cases of prior treatment strategies and devices, stabilization of a segment has been accomplished with the use of various pedicle screw constructs. Because of limitations with prior devices, the reduction of the deformity has been a challenge, and all previous instruments have been unable to allow both correction of the translation as well as application of distraction across a segment in an independent fashion. In addition, known implant systems are typically designed and configured in such a way, that one system is not easily adaptable to use the means of another system.
There are presently a number of implant systems or spondylolithesis reduction instruments known to those skilled in the art, however, none of these instruments have the flexibility to allow reduction to be performed at any level and none can perform reduction in the cervical spine. In addition, none of the current instruments allow reduction to be performed with uncoupled control of translation and distraction/compression.
One of the instruments currently available for spondylolithesis reduction is the S4 Spondylolithesis Reduction Instrument as made by Aesculap. Such an instrument or spinal system includes extended tabs whose small diameter and the polaxicity thereof maximize the range of the screw body to ease rod capture without the use of additional instruments. Such an instrument or implant system, however, does not allow reduction to be performed with uncoupled control of translation and distraction/compression.
There is described in U.S. Pat. No. 6,139,548 a sliding shaft variable length cross-link device that is for use with a dual rod apparatus such as that described in U.S. Pat. No. 5,005,562. Such a compression locking variable length cross-link device has a pair of rod hooking elements, each having rod securing and coupling ends. The coupling ends are slidably engaging by the insertion of one into the receiving socket of the other and for selective locking to one another independent of the relative separation of the rod securing ends. Each hooking element has a curvate end formed from flat material which has been shaped into a hook conformation to cup the lateral outside surface of a corresponding rod. A set screw positioned through a hole in the top of the curved end locks the curved end to the rod. In a first embodiment, one (a first) rod hooking element has a uniform cylindrical portion which may also include a knurled surface. The corresponding (second) element has a tubular portion including an axial receiving volume having an opening into which the cylindrical portion of the first element may be slidably inserted.
The exterior surface of the tubular portion of the second element includes a slotted, threaded and tapered tip which is wider at the end thereof. A nut may be engaged on the threads of the tubular portion and advanced onto the tapered portion thereof to cause the slots to narrow, crush locking the surfaces of the inner volume and the shaft together, thereby securing the two elements at a specific separation. Set screws may then be utilized to compress and lock the rods to the curved rod securing ends of each element.
There is described in U.S. Pat. No. 5,397,363, a surgical implant system for the stabilization of a human spine by fixation of the vertebra utilizing a stabilization cross-link spinal implant system. Such a system utilizes self-tapping screws having bifurcated protruding members to support an alignment rod, the protruding members available for placement of a fixed or variable traverse cross-link member that couples to the protruding members by use of threaded nuts corresponding to the threaded portion of the outer surface of the protruding members. The externally threaded coupling method can also be used for pedicle, caudal, cranial, thoracic and the like hooks. Also shown is a two plate system for anterior cervical spine fixation.
There is described in U.S. Pat. No. 5,360,431 an apparatus for the internal fixation of the spine. The apparatus includes two sets of implants each consisting of a rod and a plurality of vertebral anchors. The rod is secured to the vertebral elements by the vertebral anchors. The anchor includes a transpedicular screw which is secured to a vertebrae. The anchor further includes an anchor seat which captures the screw and permits micromotion between the anchor seat and the screw. This seat has a rod-receiving channel which captures the rod. A cap cooperates with the seat to secure the rod in the anchor. A nut screws down from the top of the assembly onto the seat to cause the rod receiving flanges in the cap to apply a compressive force to the rod. A method of therapy also is described in which the present implants are inserted surgically into a patient.
There is described in US Publication No. US 2009/0204151 a spinal implant procedure and system that includes vertical rods fastened to the spine on opposite sides. A cross connector is arranged on each vertical rod and to opposite ends of a cross member. The cross member includes a block having a lateral opening and that includes a forked end that is arranged at a bottom side of a spineous process. A strap fastener include openings through which the cross member passes. An opening of the strap fastener hooks on a catch on the side of the block. The block limits prevents rotation, blocks extension and limits flexion of the affected vertebrae.
It thus would be desirable to provide a new reduction instrument or device and methods for treating spondylolithesis using surgical techniques. It would be particularly desirable to provide such a device and method that would allow both correction of the translation as well as application of distraction across a segment in an independent fashion. Such devices/instruments preferably would be simple in construction and less costly than prior art devices and such methods would not require highly skilled users to utilize the device.